25 October 2009

Fewer large asteroids- 24OCT09

Fewer large asteroids than as predicted

And now, from the pessimists...

A fine theory and simulation. A shame it doesn't
correspond in any way to reality. The impact rate
on terrestrial planets starts out very high at the
beginning of the solar system, declines for half
a billion years then rises again in a final flurry of
accretion and clean-up, at 3.9 billion years ago.
The rate declines in a fairly uniform manner
thereafter, but about 600-to-400 million years
ago, it suddenly climbs to a level not seen since
3.4 billion years ago, and it is STILL at that
higher level today.

This is from the actual impact record, not having-
fun-with-your-computer-model science kit. The
data is from impact spherules in the lunar regolith
and the graph of the impact rates throughout
time can be found on page 660 of:

More information here:

True, this researcher thinks it might be proof of
a big comet infall due to an undiscovered companion
small star to the Sun, but so what? It might be, but
the immediate mechanism is likely to be asteroidal

The timing matches perfectly with the breakup of
the L-chondrite parent body, the largest asteroidal
breakup in the past few billion years or so. The
evidence and timing for that is presented here:

At about 480 million years ago (Ordovician times),
the meteorite fall rate on the Earth was 100 TIMES
GREATER than it is today, during the peak of that
breakup episode.

The history of the formation of the 50 or so asteroidal
families unambiguously identified does not match this
pretty little theory in the least. Reality is contingent,
accidental, and randomly chaotic, and NOT "well
described with a logarithmic decay law."

Source: Sterling K. Webb, USA

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